ACTG 250 To determine bioavailability, pharmacokinetics, safety and tolerance of single doses of nevirapine in HIV infected pregnant women and their newborns when the drug is given during labor, to determine the same in neonates dosed during the first week of life and whose mothers also received nevirapine, and to determine short-term safety profile of neonates who received no dose, a single dose or multiple doses. Also, to determine resistance to nevirapine and penetration of drug into breast milk.